* Biggest consistent block of losers is S-values that are more than one higher than the T of the target, up to the point where S = 2*T; in these cases, they are wounding on 3+ when previously they would have wounded on 2+. This has the most pronounced effect on S5 vs T3 and S6-7 vs T4, which used to be very reliable at generating wounds against infantry targets. This is one of the two reasons by brainleech devourers are no longer the kings of Tyranid shooting (the other being the change from AV to T+Sv+Wds).

* Similarly, the biggest winners under the new scheme is for S value at T-2 or lower; they are going from 6+ to 5+ (in most cases) or gaining the ability to wound at all (for S more than 3 lower than T). This effect is most pronounced for the lowest S values (S2, only seen in the strangleweb, has improved dramatically and would be great against and diminishes as it goes up (S5 is the highest value where the net gain against T7-8 balances out the loss against T3; higher S-values only gain against unrealistically high T and lose against very common T4-5).

* Nearly all Strength values are now better against nearly all vehicles. In particular, S2-7 are capable of wounding vehicles that would previously have been immune, and some specific pairings (S4 vs. AV10->T6, S5 vs. AV11-> T7, and S6 vs. AV12->T8) are now twice as effective as previous due to the spreading out of the 3+ to wound zone. S4 and S5 are the biggest winners here, although S8-10 vs. anything that was AV14 before and is now T8 is also really great.

* The only losers against vehicles are in very high S-values against low AV. Where previously, S9+ was automatically getting at least a glance against AV10, now it's only wounding the T6 on a 3+ and still has to get through the armor save. This applies to S8 vs. AV10 (T6), S9 vs. AV10-11 (T6-7), and S10 vs. all vehicles (T6-8).

This analysis is complicated by the fact that the correlation between AV values and the new vehicle T values is imperfect; it appears that AV10 all-around vehicles are now T6, majority AV11 are now T7, and anything higher is T8. However, the inclusion of vehicle armor saves, massive increases in W (compared to HP before), and the addition of damage values (since all vehicles have 6+ wounds) makes it difficult to say what is better or worse than before EXCEPT for weapons that previously had no chance of hurting vehicles and now have at least a small chance. This is a net benefit for mid-to-low strength weapon that put out lots of shots (i.e. devourers on gaunts).

Of note, now that blast weapons cause variable numbers of hits they are now very much worth considering as anti-vehicular weapons (where previously they were always terrible because they could only hit one time, and weren't Strong enough to get a reliable penetrating hit). Combined with the Strength and/or AP improvements to the venom cannon, barbed strangler, and stranglethorn cannon, all of these are now much more viable for their fluff-intended role.

Toughness values:Similar arguments as above for Strength due to the new spread of To Wound rolls.

* Mathematically, the biggest winners in Toughness are T4, T5, and T6, although the net change from the old system is pretty tiny. Mainly, the reduction in To Wound rolls for S6-7 vs T4, and S7+ vs T5, and S8+ vs. T6 make these toughness values much more survivable against mid-strength high-volume attacks without losing anything to low-Strength (with the notable exceptions of T5 vs S3 and T6 vs S4, both of which are much less survivable than before). This effect will swing mostly on whether you expect to see more lasguns (worse) or autocannons (better) in the opposing force.

* The high-water mark for improvement to survivability is between T5 and T6; going both up and down from there reduces this advantage, although it doesn't get worse than 7e until you get to T2 and below (spore mines only, I think) and T9 (unheard of, certainly in the Tyranid army).

Save values:

* Big winner is Sv4+, which now is getting saves against weapons that were formerly AP4 and AP3, and is no worse off against weapon that were formerly AP5, 6, and -- because they're all AP0 now. Basically, you need an AP1 or 2 weapon (now AP-4 and AP-3) to fully penetrate Sv4+.

* Sv5+ has improved nearly as much, mainly because AP5 (AP0) no longer penetrates it, and AP4 (AP-1) still permits some save. Better APs are no different from previous.

* Sv3+ is just as much better as Sv5+, for similar reasons. Although it is worse against AP4 (AP-1), it is clearly better against AP3 (-2) and AP2 (-3) which used to cut right through it, and those APs are common to mid-to-high strength weapons that are likely to be pointed at a Sv3+ MC.

* Sv6+ is slightly better than before, due to the changes to AP5/6/-- turning to AP0, but can't improve that much because Sv6+ just isn't that good to begin with.

* Sv2+ has very mixed results; although it is significantly worse than before against AP3 (-2) and AP4 (-1), it also gets back a chance to save against AP2 (-3) and AP1 (-4) which balances out. The relative value of this will depend on the prevalence of each AP value in the opposing army (and since AP-2 and worse is probably going to be more common than AP-3 and AP-4, Sv2+ has probably gotten worse in aggregate). Not that this is relevant to Nids because not even the Tyrannofex has a 2+ armor save anymore.

Of note, all save values either stayed the same or got better, meaning overall, more wounds are being saved than in the previous edition. This is consistent with the overall sense that more Armor Save values are getting reduced saves instead of just being negated.

AP values:(this assumes that all weapons went from AP1 = AP-4, AP2 = AP-3,...AP5+ = AP0; this is not universally true, but definitely the overwhelming majority)

* Only AP- has remained the same (obviously); in all other cases, the translation from negating certain armor saves in 7e to modifying the save roll in 8e has made the equivalent AP value worse (concurring with the conclusion above that more wounds are, on the whole, being saved).

* The biggest loser is AP5 (0), which used to negate Sv5+ and 6+ and now does nothing. Especially considering all of the models out there with 5+ or 6+ saves, this is a huge blow to the effectiveness of fleshborers, bolters, and similar weapons.

* AP2 (-3) is the next most harmed. Where is used to negate all armor saves, now it permits a save from Sv3+ and Sv2+. It's still completely negating Sv4+ and worse, which isn't bad, but not incredibly relevant since you're mainly throwing these attacks at high-Toughness targets with good armor saves (good AP is usually paired with high S).

* AP1 (-4), AP3 (-2), AP4 (-1), and AP6 (0) are all still in the same ballpark as 7e; their value has gone down a little, but close enough to previous that it will be strongly dependent on the sorts of saves in opposing armies. In particular, AP4 (-1) gets increasingly good as the average opposing save gets better (vs. Sv3+ in particular, where it used to have no effect)

On the whole, I can say that in an all-comers army, survivability has improved for both Toughness and Armor Saves as a whole, and specifically in ranges that are important to Tyranids (Sv3+, 4+, and 5+, T3, 4, 5, and 6). The next analytical step would be to compare survivability-per-point (including T, Sv, W, and other defensive capabilities) with other armies' forces to figure out whether Nids can compete in the durability contest, or whether they need to win through killing the enemy. That is an assessment for another time, and probably better accomplished through play.

_________________"And Darkness and Decay and the Red Death held illimitable dominion over all."
- Edgar Allen Poe, The Masque of the Red Death